Punjab PSEB Matric Science flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

pH scale

A 0–14 scale measuring hydrogen-ion concentration; values below 7 are acidic, above 7 basic, and exactly 7 neutral at 25 °C.

Neutralisation reaction

Reaction in which an acid and a base combine to form salt and water only, releasing heat; for example HCl + NaOH gives NaCl + H₂O.

Baking soda

Common name for sodium hydrogen carbonate, NaHCO₃; used in baking powder, antacids and fire extinguishers, and on heating it gives sodium carbonate, carbon dioxide and water.

Reactivity series of metals

Arrangement of metals in decreasing reactivity: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au; metals above hydrogen displace it from dilute acids.

Amphoteric oxide

Metal oxide that reacts with both acids and bases to give salt and water; aluminium oxide and zinc oxide are the standard examples.

Graphite

Carbon allotrope of stacked hexagonal layers; each atom bonds to three neighbours, leaving one delocalised electron, so graphite conducts electricity and feels slippery.

Photosynthesis

Process in chloroplasts where green plants use sunlight and chlorophyll to convert carbon dioxide and water into glucose and oxygen: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

Anaerobic respiration in yeast

Breakdown of glucose without oxygen producing ethanol, carbon dioxide and little energy; this fermentation is used in baking, brewing and industrial alcohol production.

Reflex arc

Route taken by nerve impulses in a quick involuntary response: receptor, sensory neuron, spinal cord relay, motor neuron, effector muscle; the brain is informed afterwards.

Insulin

Hormone made by beta cells of the pancreas that lowers blood glucose by stimulating uptake into cells; its deficiency or ineffectiveness causes diabetes mellitus.

Placenta

Disc-like tissue attached to the uterine wall that lets glucose, oxygen and nutrients pass from mother to embryo while fetal wastes diffuse back into maternal blood.

Monohybrid F2 ratio

When two heterozygous F1 plants are crossed, offspring show a 3 : 1 phenotypic ratio of dominant to recessive and a 1 : 2 : 1 genotypic ratio.

Homologous organs

Organs with the same basic structure and origin but different functions, such as human arm and bat wing; they indicate divergent evolution from a common ancestor.

Laws of reflection

The angle of incidence equals the angle of reflection, and the incident ray, reflected ray and normal all lie in one plane on opposite sides of the normal.

Mirror formula

1/v + 1/u = 1/f links image distance, object distance and focal length for a spherical mirror; magnification m = −v/u = image height / object height.

Snell's law

For light crossing a boundary between two media, sin i / sin r is constant, equal to the refractive index of the second medium relative to the first.

Power of a lens

Reciprocal of focal length measured in metres, P = 1/f, expressed in dioptres; a convex lens has positive power and a concave lens negative power.

Myopia

Near-sightedness in which the image of a distant object forms in front of the retina, so far objects look blurred; it is corrected by a concave lens.

Critical angle

Angle of incidence in the denser medium for which the refracted ray grazes the surface; beyond it total internal reflection occurs instead of refraction.

Tyndall effect

Scattering of a light beam by fine colloidal particles, making its path visible; it explains the blue sky and the reddish sun at sunrise and sunset.

Ohm's law

At constant temperature the current through a metallic conductor is directly proportional to the potential difference across it, so V = IR with R in ohms.

Resistivity

Material property used in R = ρL/A and measured in ohm-metre; it depends on the material and temperature, not on the wire's length or thickness.

Parallel combination

Circuit arrangement in which each resistor receives the full supply voltage while current divides; 1/R = 1/R₁ + 1/R₂ + …, so total resistance is smaller than any branch.

Electric power

Rate at which electrical energy is consumed, P = VI = I²R = V²/R, measured in watts; one kilowatt-hour equals 3.6 × 10⁶ joules.

Fleming's left-hand rule

Rule giving the direction of force on a current-carrying conductor in a magnetic field: forefinger along field, middle finger along current, thumb shows thrust.

Split-ring commutator

Device in a DC motor or generator that reverses the coil's connections every half rotation, so the current in the external circuit stays unidirectional.

Five Rs

Waste-management hierarchy of refuse, reduce, reuse, repurpose and recycle; it prefers avoiding waste creation over treating or dumping waste later.

Joint Forest Management

Scheme in which village communities protect degraded forest land together with the forest department and receive a share of produce such as fuelwood and fodder.

Ten per cent law

Only about ten per cent of the energy at one trophic level passes to the next; the rest is lost mainly as heat, so food chains have few levels.

Biomagnification

Progressive increase in the concentration of non-biodegradable pollutants such as pesticides at higher trophic levels, because organisms store them in fat instead of excreting.

Acid rain

Rain or snow with pH below 5.6, formed when sulphur dioxide and nitrogen oxides from burning fossil fuels dissolve in atmospheric moisture and fall as dilute acids.

Ozone depletion

Thinning of the stratospheric ozone layer by chlorofluorocarbons and halons, allowing more ultraviolet radiation to reach the earth and raising skin cancer and crop damage.